I've got this grin smiley during the upgrade process to Windows 10 Mobile.
The solution was to use Microsoft Device Recovery Tool (earlier known as Microsoft Windows Phone Recovery Tool).
That's what I did:
1. Downloaded Microsoft Device Recovery Tool.
2. Attached the phone to the PC, opened Recovery Tool and waited for the connection.
Since the phone was in the loop boot state (it automatically was rebooting itself after the blue screen), I waited until the phone restarted itself. On one of the restarts the Tool recognized the phone. Luckily, the phone didn't continue to boot and didn't fall into BSOD. It stayed connected to the PC.
3. The Tool recognized phone's model and started to flash.
4. All of a sudden, phone's screen turned black and the flash procedure failed.
5. I removed the battery and inserted it back. The phone stopped being recognized by the tool. However, it registered itself with the tool and its record was present in the tool's list of known devices.
6. I clicked the Phone wasn't recognized button and waited until the Tool reflashes phone's bootstrapper. No luck.
7. I did several retries and on one of the retries the phone started with red Nokia brand. It meant, the tool reflashed bootstrapper part of the firmware.
8 Finally, after flashing the new bootstrapper, the Tool reconized the phone; I reflashed to phone with the new OS ROM.
Hope this helps.